1. Field
The present disclosure relates generally to manufacturing parts and, in particular, to a method and apparatus for manufacturing hardened metallic structures. Still more particularly, the present disclosure relates to a method and apparatus for manufacturing a precipitation hardened metal alloy structure for transmission gear applications.
2. Background
A gear is a component that may be found within a transmission system that may transmit rotational force to another gear and/or device. A gear may take the form of a rounded wheel with teeth. The teeth may engage and/or mesh with other teeth on another gear and/or device. This engagement may allow for force to be transferred from one gear to another gear and/or device without slippage.
Gears are commonly found in various vehicles, such as an aircraft. In particular, a helicopter has a number of different transmission systems in which gears are used. For example, without limitation, a helicopter has one or more of an engine nose transmission box, an intermediate gear transmission box, a main transmission gear box, a tail rotor transmission box, or some other suitable gear system.
Gears for industrial and/or aerospace applications typically have a strong, tough core. This core is designed to be resistant to crack propagation and roller fatigue failure. The surface of a gear typically has a strong, hard layer that forms the teeth for the gear. This surface is designed to be resistant to wear that can occur from the surface of the teeth of the gear sliding against teeth on another gear and/or device.
These properties for gears are achieved using various types of metals and/or metal alloys. For example, without limitation, steel alloys are processed by quenching and tempering steel alloys followed by nitrating of the alloys. In addition to having these types of properties, it also is desirable to decrease the weight of gears, especially for use in aerospace applications. For example, without limitation, gears in a helicopter transmission may form around one third of the weight of the systems.
One solution is to use a titanium gear. A titanium gear has a lower density as compared to steel alloys, resulting in a lower weight. Currently available titanium alloy gears, however, have a lower strength than a steel alloy gear with similar dimensions. For example, without limitation, gears made from widely available titanium alpha-beta alloys, such as Ti-6Al-4V or Ti-6Al-2Sn-4V-2Zr, have a strength that is one third less than a steel alloy gear.
To compensate for this type of strength difference, a titanium alloy gear may be thicker to compensate for the lower strength. This compensation, however, often reduces the weight savings enabled by the lower density of titanium alloys, to near zero. Further, titanium alloy gears also have surfaces that are not as hard as the surfaces of steel alloy gears with respect to resisting sliding wear when engaging other gears.
Therefore, it would be advantageous to have a method and apparatus that takes into account one or more of the issues discussed above, as well as possibly other issues.